Vibration-dampening drill collar

ABSTRACT

A drill collar primarily for use with measurement-while-drilling and logging-while-drilling sensors, the drill collar composed of a non-magnetic nickel alloy, and having three or four elongate nitral elastomer ribs parallel the longitudinal axis and mounted on the inner surface of the drill collar, defining a central aperture for receiving the down-hole sensor and inter-rib apertures for receiving drilling fluid. This novel drill collar is especially useful in rough or underbalanced drilling applications, protecting the sensor and enhancing measurement accuracy by dampening flow-based harmonic vibrations, absorbing vibration from lateral tool movement, and stabilizing/centralizing the sensor within the central aperture. Also, the novel drill collar allows the operator to run lower fluid rates while drilling, minimizing formation damage from fluid invasion.

FIELD OF THE INVENTION

The present invention relates generally to apparatus for protecting down-hole tools such as sensors during drilling, and more particularly to apparatus for protecting down-hole sensors from the effects of vibration produced when drilling a well.

BACKGROUND OF THE INVENTION

In typical drilling systems utilized in the oil and gas industries, a rig is established at a desirable location, the rig comprising a rotatable drill string (consisting of drill pipe sections and heavier drill collars, the latter fitting around the lower drill pipe) and a drill bit at the down-hole end. During drilling, this rotatable component of the rig is rotated from the surface, causing the drill bit to cut into the downwardly adjacent rock formations, with the weight of the drill collar assisting in driving the drill bit downward into contact with the underlying rock. Drill collars also act as conduits for the drilling fluids used to lubricate the drill bit and carry cuttings back to the surface. Mud motors and turbines are sometimes employed down-hole to aid the drill bit rotation.

At various points during drilling, specialized measurement and telemetry tools can be employed to assess conditions in the rock formations adjacent the wellbore. Methods well known in the art include measurement-while-drilling (MWD) and logging-while-drilling (LWD), which methods employ a diverse and evolving range of sensors. These sensors are usually located in the drill string near the drill bit, with the derived data from such sources as resistivity, gravity, magnetic and nuclear magnetic resonance measurements being stored in down-hole memory or transmitted to the surface.

While such sensors provide highly useful information about the down-hole drilling environment, vibration due to the drilling process can damage the sensors. An axial load is applied to the drill bit during drilling into underlying formations, and this produces vibrations in the overlying drill string, and vibration can occur due to drill string rotation in deviated or directional wellbores. Also, drilling fluid flow around the tool can initiate harmonic vibrations and side-to-side “slapping” of the tool ensues. While most of these sensors are sufficiently robust to address the vibrations of normal drilling conditions, a variety of attempts have been made to counter the potentially damaging vibrations.

U.S. Pat. No. 4,522,271 to Bodine et al., for example, teaches a sonic damper unit which is placed directly above a drill collar string to damp out unwanted complex wave vibrations of the string both longitudinal and lateral in vibration mode, the damper unit comprising a tubular section filled with small pieces of material capable of motion in a random pattern and thereby responding to the frequency content to damp out unwanted vibrational energy. In another example, U.S. Pat. No. 6,429,653 to Kruspe et al. discloses a method and apparatus for protecting a sensor from impact and abrasion, including a drill collar having a section of electrically non-conductive material, the sensor being located inside the drill collar within the section of electrically non-conductive material. Kruspe et al. alternatively disclose placing the sensor in a removable probe fitted with protective stabilizers. A variety of other shock absorbing devices are also known in the art, such as mechanical stabilizing projections mounted on the tool.

However, existing means to dampen drill string vibrations or provide shock absorption suffer from numerous disadvantages, including high manufacturing cost, failures of inherently unreliable “point-contact” mechanical shock absorbers (such as belly springs), and the requirement for a significant drilling fluid throughflow to support certain stabilization devices (which can result in formation damage from fluid invasion). Also, in rough or underbalanced drilling environments, conditions are such that excessive vibration can defeat currently known tool protection means.

What is therefore required is a means for addressing the problem of down-hole vibration (from the drill bit as well as harmonic vibration) and resultant tool damage, the means being relatively inexpensive to manufacture, preferably more reliable than point-contact mechanical stabilizers and capable of effective use in rough or underbalanced environments, and not requiring reliance on significant fluid flow to support the stabilization of the down hole tool.

SUMMARY OF THE INVENTION

It is an object of the present invention, therefore, to provide a simple apparatus effective in dampening down-hole vibration in the tool-housing region of a drill string, even in rough or underbalanced drilling environments, while not requiring significant fluid flow for its utility.

According to a first broad aspect of the present invention, there is provided a drill collar for use with a down-hole tool, the drill collar comprising: a hollow, cylindrical sleeve having a longitudinal axis and an inner surface facing towards the longitudinal axis; and a plurality of elongate ribs parallel to the longitudinal axis and mounted on the inner surface in spaced-apart arrangement, defining thereby a central aperture within the sleeve for receiving the down-hole tool and inter-rib apertures for receiving drilling fluid.

According to a second broad aspect of the present invention, there is provided a vibration-dampening apparatus for use with a down-hole tool used in measurement-while-drilling and/or logging-while-drilling applications, the vibration-dampening apparatus comprising: a drill collar comprising a hollow, cylindrical sleeve having a longitudinal axis and an inner surface facing towards the longitudinal axis; and a plurality of elongate ribs parallel the longitudinal axis and mounted on the inner surface of the drill collar in spaced-apart arrangement, defining thereby a central aperture within the drill collar for receiving the down hole tool and inter-rib apertures for receiving drilling fluid.

According to a third broad aspect of the present invention, there is provided a drill collar for use with a measurement-while-drilling and/or logging-while-drilling sensor, the drill collar comprising: a hollow, cylindrical sleeve having a longitudinal axis, an inner surface facing towards the longitudinal axis, and a box end and a pin end at opposed ends of the sleeve, the sleeve composed of a non-magnetic nickel alloy; and four elongate ribs parallel to the longitudinal axis and mounted on the inner surface in spaced-apart arrangement, defining thereby a central aperture within the sleeve for receiving the sensor and inter-rib apertures for receiving drilling fluid, the elongate ribs extending along substantially the entire length of the sleeve and composed of a nitral elastomer.

In exemplary embodiments of the present invention, the down-hole tool is a sensor used in measurement-while-drilling and/or logging-while-drilling applications. The sleeve is preferably composed of a non-magnetic material, and most preferably a nickel alloy, and the sleeve preferably but not necessarily comprises a box end and a pin end at opposed ends of the sleeve, while double box end or double pin end connections may be used in some preferred embodiments. The elongate ribs are preferably composed of an elastomeric material, most preferably a nitral elastomer. The ribs are preferably three or four in number, depending primarily on sleeve dimensions, the ribs preferably equally spaced around the inner surface of the sleeve and preferably but not necessarily extending along substantially the entire length of the sleeve.

This novel drill collar is especially useful in rough or underbalanced drilling applications, supporting and centralizing the sensor and enhancing measurement accuracy by dampening flow-based harmonic vibrations, absorbing vibration from lateral tool movement, and stabilizing/centralizing the sensor within the central aperture. Also, the novel drill collar allows the operator to run lower fluid rates while drilling, minimizing formation damage from fluid invasion.

A detailed description of an exemplary embodiment of the present invention is given in the following. It is to be understood, however, that the invention is not to be construed as limited to this embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:

FIG. 1 is a cut-away side elevation view of a drill collar according to the present invention, showing the positioning of the elongate ribs in relation to the longitudinal axis of the drill collar;

FIG. 2A is a cross-sectional view of the drill collar of FIG. 1 along line 2-2, illustrating the use of four elongate ribs; and

FIG. 2B is a cross-sectional view similar to FIG. 2A but illustrating the use of three elongate ribs.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Referring now in detail to the accompanying drawings, there is illustrated an exemplary embodiment of a drill collar according to the present invention generally referred to by the reference numeral 2.

The exemplary drill collar 2 is for use with measurement-while-drilling and/or logging-while-drilling sensors (not shown) employing electro-magnetic transmission modes, the drill collar 2 comprising a hollow, cylindrical sleeve 4 having a longitudinal axis 6. The sleeve 4 has an inner surface 8 facing towards the longitudinal axis 6, and a box end 16 and pin end 18 at opposed ends of the sleeve 4 for connecting the drill collar 2 to adjacent string sections (not shown) (although double box end or double pin end connections may be used in some preferred embodiments). In this exemplary embodiment, the sleeve 4 is composed of a non-magnetic nickel alloy such as Monel™, although other non-magnetic materials may be suitable in various contexts. In exemplary embodiments, the drill collar 2 may be from 2 to 12 metres in length, depending on tool requirements, with an outside sleeve 4 diameter accordingly ranging from 89 to 229 mm, and an internal sleeve 4 diameter accordingly ranging from 57 to 82.55 mm. Multiple collar sizes will be required to address different hole sizes, flow rates, and MWD/LWD tool sizes. The following table provides dimensions for a variety of drill collars 2 according to the present invention, including preferred rib 10 numbers: Minimum Maximum Sleeve Sleeve Outside Sleeve Internal Sleeve Number of Length Length Diameter Diameter Elongate Ribs 2 metres 9.5 metres   89 mm   57 mm 3 or 4 2 metres 9.5 metres 95.25 mm   57 mm 3 or 4 2 metres 9.5 metres   121 mm   57 mm 4 3 metres  12 metres   159 mm 71.44 mm 4 3 metres  12 metres   165 mm 71.44 mm 4 3 metres  12 metres   171 mm 71.44 mm 4 3 metres  12 metres 177.8 mm  76.2 mm 4 or 5 3 metres  12 metres 190.5 mm  76.2 mm 4 or 5 3 metres  12 metres   203 mm  76.2 mm 5 3 metres  12 metres   229 mm 82.55 mm 5 or 6

Referring now to FIGS. 2A and 2B, the drill collar 2 is provided with a plurality of elongate ribs 10. In FIG. 2A, there are four ribs 10, spaced evenly apart on the inner surface 8 of the sleeve 4. In FIG. 2B, there are three ribs 10, again spaced evenly apart on the inner surface 8 of the sleeve 4. The required flow area (determined by collar size and drilling flow requirements) will determine the number and size of elongate ribs 10 required in a given application, with six ribs 10 for the largest collar 2 lengths (see the above table). The elongate ribs 10 are permanently attached to the inner surface 8 and are parallel the longitudinal axis 6, thereby defining a central aperture 12 (best seen in FIGS. 2A and 2B) within the sleeve 4 for receiving the down-hole tool; this central aperture 12 has a diameter of 44.5 to 47.63 mm depending on tool clearance requirements. The positioning of the elongate ribs 10 also results in inter-rib apertures 14, best seen in FIGS. 2A and 2B, for receiving drilling fluid (not shown).

In the exemplary embodiment, the elongate ribs 10 extend along substantially the entire length of the sleeve 4 and are composed of a nitral elastomer; this is the same elastomer that is used with some mud motor stators. Elastomeric material is known in the art for its ability to absorb energy from vibration and impact (for example, U.S. Pat. No. 6,102,142 to Besson et al.). The ribs 10 support the cylindrical tool along its entire length, not just at contact points as is the case with current mechanical stabilizers, so the tool does not start moving and causing harmonic vibrations. The present invention accordingly does not require the minimum fluid rates used in a multiphase flow in underbalanced drilling applications to stabilize and protect the tool, which therefore minimizes formation damage from fluid invasion. It has been found, in fact, that only minor lubrication is required to work this invention. Where a specific desired elastomer may swell due to the presence of certain fluids, or experience possible down-hole temperature limitations where hot hole conditions are encountered, a special elastomer may be required.

In addition to being composed of a relatively inexpensive material, the manufacturing process is relatively simple and akin to known elastomer processes in mud motor contexts; the existing process for building a mold for injecting mud motor stators can be employed to inject the drill collars 2. A mold (not shown) will incorporate three or more rib voids based on the required flow data. The drill collar 2 is then prepared for the mold and a bonding agent (not shown) is prepared and installed on the inner surface 8 of the drill collar 2. The mold is then inserted into the drill collar 2 and an elastomeric material is injected into the drill collar 2 with the mold seated therein. The elastomeric material then sets and adheres to the inner surface 8, and the mold is removed, creating a set of elastomeric ribs 10 that run substantially the entire length of the drill collar 2. When the elongate ribs 10 wear down from prolonged use, the drill collar 2 can be provided with replacement ribs 10 using the same process.

The present invention is especially useful in underbalanced applications, and also with coalbed methane drilling. The elastomeric fins 10 will both centralize the tool and dampen vibration during the drilling process in single phase or multiphase flow regimes. The result is a stable environment in which the sensor can conduct measurements, with a significantly reduced risk of tool damage due to vibration. Tool life and performance are accordingly enhanced by use of the present invention.

A prototype according to the present invention was tested for performance, and test drillings without a drill collar according to the present invention were conducted for the sake of comparison. The present invention was found to significantly enhance the tool life. The test drillings were conducted with an electromagnetic MWD tool in an underbalanced drilling medium, a hole size of 6¼″ (159 mm), and a drilling medium comprising 5 gallons/min. (20 litres/min.) fluid and 1300 cfm (36.8 cubic metres/min.) gas. Two test runs were conducted without a drill collar according to the present invention, g values were measured up to 125×g (the force exerted by gravity), and catastrophic tool failure occurred within a matter of minutes on both test runs. In a test run conducted with a drill collar according to the present invention, 9 values were measured at 2 to 4×g during drilling, and there was no tool failure. During the test run of the drill collar according to the present invention, the drilling fluid was reduced near the bottom of the well, and even when running “dry” the g values did not exceed 7×g. These results accordingly indicate up to 18 to 31 times potential reduction in vibration when utilizing the present invention.

While a particular embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention and are intended to be included herein. It will be clear to any person skilled in the art that modifications of and adjustments to this invention, not shown, are possible without departing from the spirit of the invention as demonstrated through the exemplary embodiment. The invention is therefore to be considered limited solely by the scope of the appended claims. 

1. A drill collar for use with a down-hole tool, the drill collar comprising: a hollow, cylindrical sleeve having a longitudinal axis and an inner surface facing towards the longitudinal axis; and a plurality of elongate ribs parallel the longitudinal axis and mounted on the inner surface in spaced-apart arrangement, defining thereby a central aperture within the sleeve for receiving the down-hole tool and inter-rib apertures for receiving drilling fluid.
 2. The drill collar of claim 1 wherein the down-hole tool is a sensor used in measurement-while-drilling and/or logging-while-drilling applications.
 3. The drill collar of claim 1 wherein the sleeve is composed of a non-magnetic material.
 4. The drill collar of claim 3 wherein the non-magnetic material is a nickel alloy.
 5. The drill collar of claim 1 wherein the sleeve further comprises a box end and a pin end at opposed ends of the sleeve.
 6. The drill collar of claim 1 wherein the elongate ribs are composed of an elastomeric material.
 7. The drill collar of claim 6 wherein the elastomeric material is a nitral elastomer.
 8. The drill collar of claim 1 wherein the elongate ribs are equally spaced around the inner surface.
 9. The drill collar of claim 1 wherein there are four elongate ribs.
 10. The drill collar of claim 1 wherein the elongate ribs extend along substantially the entire length of the sleeve.
 11. A vibration-dampening apparatus for use with a down-hole tool used in measurement-while-drilling and/or logging-while-drilling applications, the vibration-dampening apparatus comprising: a drill collar comprising a hollow, cylindrical sleeve having a longitudinal axis and an inner surface facing towards the longitudinal axis; and a plurality of elongate ribs parallel the longitudinal axis and mounted on the inner surface of the drill collar in spaced-apart arrangement, defining thereby a central aperture within the drill collar for receiving the down-hole tool and inter-rib apertures for receiving drilling fluid.
 12. The vibration-dampening apparatus of claim 11 wherein the drill collar is composed of a non-magnetic material.
 13. The vibration-dampening apparatus of claim 12 wherein the non-magnetic material is a nickel alloy.
 14. The vibration-dampening apparatus of claim 11 wherein the drill collar further comprises a box end and a pin end at opposed ends thereof.
 15. The vibration-dampening apparatus of claim 11 wherein the elongate ribs are composed of an elastomeric material.
 16. The vibration-dampening apparatus of claim 15 wherein the elastomeric material is a nitral elastomer.
 17. The vibration-dampening apparatus of claim 11 wherein the elongate ribs are equally spaced around the inner surface.
 18. The vibration-dampening apparatus of claim 11 wherein there are four elongate ribs.
 19. The vibration-dampening apparatus of claim 11 wherein the elongate ribs extend along substantially the entire length of the sleeve.
 20. A drill collar for use with a measurement-while-drilling and/or logging-while-drilling sensor, the drill collar comprising: a hollow, cylindrical sleeve having a longitudinal axis, an inner surface facing towards the longitudinal axis, and a box end and a pin end at opposed ends of the sleeve, the sleeve composed of a non-magnetic nickel alloy; and four elongate ribs parallel the longitudinal axis and mounted on the inner surface in spaced-apart arrangement, defining thereby a central aperture within the sleeve for receiving the sensor and inter-rib apertures for receiving drilling fluid, the elongate ribs extending along substantially the entire length of the sleeve and composed of a nitral elastomer. 